EMBANKMENT OF SOFT SOIL, INTERACTION BETWEEN EMBANKMENT REINFORCEMENT AND PILES. LONG TERM MEASUREMENT AT URVALLA, SWEDEN

Railroad embankments on soft ground are often supported by so-called embankment piles, i.e. piles with pile caps. However, if the subsoil is very soft, the embankment is often founded on piled rafts instead due to the risk of failure and settlements between the pile caps. At Urvalla, the subsoil was very soft, and since a piled raft was found to be very expensive, a new design method was tested. Two layers of polyester grids were placed just above the pile caps. The design of such construction is highly sensitive to the vertical deflection that can be considered acceptable between the pile caps. In order to verify the design model, two sections were instrumented to monitor the deflection of the grids between the pile caps, and the strain of the grids. Measurements have been made since 1995 and after three years, the deflection of the grids between the pile caps is about 60 mm (2.3 in) and the maximum strain is about 1.4%, which confirms the acceptability of the design.